Death knight alt gearing up as blood and getting ready for ToT

Hello everyone, my DK just dinged 90 a few days ago, I know tanks are hardest to gear up because pvp items are less useful for tank due to lack of defensive stats. I've been reading here that DKs avoiding defensive stats as much as they could but does that applies to low gear levels too? I'm gonna tank in my guild's alt runs soon, they are at 4 heroics so I will be undergearead for it for a while, should I focus stamina-defensive stats when I'm undergeared or just go for mastery-haste?

DKs do not avoid defensive stats as much as they could. Lots of DKs prioritize Accuracy > Mastery > Haste > Avoidance for tanking. As long as the gear has str/stam and hit/exp/mastery/haste on it you can consider it "fit for LFR" tanking gear. (yes, even hit/haste, hit/exp or exp/haste work) When you get your hands on more gear you just want to try to maximize the mastery you get out of it and you should be fine. (I've tanked ToT LFR in ~480 DpS blues with less than 100% mastery and no dodge/parry on gear, though the success depends on your healers)

If you seek to minimize damage taken, you'd want for Mastery>Avoidance>Hit>Exp>Haste.

But before you go and tank raids, try some practice runs in heroics and such to keep others from comiting mental suicide if they have you as tank

I meant dodge and parry as defensive stats and as I read from here I see most of good geared DKs getting as much mastery and haste as they can so I thought they are avoiding it.

I have some pratice from leveling blood with mostly dungeons and having a max level DK on last 2 expansions but I might go for minimum damage taken build because I will be undergeared most likely. What about gems for minimizin damage taken? Still go for mastery or change to stamina?

I can't say much about tanking Horridon HC as MT, our Pala is tanking him, reseting after every 6th stack.
Im tanking Tortos Heroic with iLvl 330 Haste/Crit Gear, unbuffed 29% haste, 19% crit and 95% mastery.
We're two healing Tortos, 60% of the Healing im recieving i get by myself, 300k dps done on Tortos Single Target and never have survivability problems,
even if we're wiping i'm the last standing when healers down... crystal shell nerly never drops, and if instant macro for deathcoil on the crystal, deathstrike and healthstone and everythings fine.

Tanked almost a full hm 25 man clear including our first lei shen 25hm kill on my just hit 90 DK. Our other tank 1 tanked durumu and Iron Qon since we always 1 tank those, and i played my main (also a tank) for DA and primordius as those are sometimes rocky for us, but i legitimately tanked the other 8 bosses. But yeah, we really, really, wanted a second gorefiend's grasp for HM lei shen, so we cleared with my dk tanking, starting at a 495 ilvl. We extended, and killed 25 HM Lei shen with my dk up to a 522 ilvl from another week of lfr and the the prior week's heroic clear, including an intellect cape (the mastery and stamina jump over a 483 str-avoidance cape was worth it imo) and an agility ring (same story as the cape). DKs are very, very not gear dependent. At even gear, tanking the content that you're actually supposed to do in that gear, I would take my monk over my DK any day of the week, but pretty sure it would have been a lot harder to tank hm lei shen 25 on a 522 monk than a 522 dk was. Timing death strikes and rotating your ridiculous array of cool downs appropriately is so much more important than your gear as a death night.

That being said, at your level of gear, nearly anything is going to be an upgrade. I'd highly suggest ignoring stamina other than maybe a trinket, going for mastery > hit>exp>avoidance>haste, but nearly always taking a higher ilvl item regardless of stats (not counting crit) unless it's just barely a higher ilvl. Once you're not in much danger of dying, then start looking at moving haste up that chart, but frankly just starting out, you're unlikely to be using the haste that well anyway. Just, whatever you do, get used to the idea of just sitting there banking your f/u runes, only using blood runes and rp, hitting nothing some of the time, waiting for a substantial hit to land, then death strike. If both pairs of f/u runes are recharging, make sure you keep a blood rune ready to rune tap. Rotating through your cds, and using your runes carefully is way more important than what stats you have on your gear.